Ethers of aromatic acids are useful as intermediates and additives in the manufacture of many valuable materials including pharmaceuticals and compounds active in crop protection, and are also useful as monomers in the production of high-performance rigid rod polymers, for example, linear rigid oligoanthranilamides for electronic applications [Wu et al, Organic Letters (2004), 6(2), 229-232] and polypyridobisimidazoles and the like [see e.g. Beers et al, High-Performance Fibres (2000), 93-155].
Existing processes to produce 2,5-dialkoxy- and 2,5-diarenoxyterephthalic acid involve stepwise alkylation of 2,5-dihydroxyterephthalic acid to form the corresponding 2,5-alkoxy- and 2,5-diarenoxyterephthalic esters followed by dealkylation of the ester to the acid. An n-hydroxy aromatic acid may be converted to an n-alkoxy aromatic acid by contacting the hydroxy aromatic acid under basic conditions with an n-alkyl sulfate. One suitable method of running such a conversion reaction is as described in Austrian Patent No. 265,244. Yields are moderate to low, productivity is low and a two-step process is necessary.
A need therefore remains for a process by which ethers of aromatic acids can be produced economically and with high yields and high productivity in small- and large-scale operation, and in batch and continuous operation.